1. Field of the Invention
The present invention relates to a magnetic disc apparatus.
2. Description of the Related Art
Currently, with the advance of personal computers and work stations, a hard disc drive has an increased capacity and reduced size, which requires a high-density recording of a magnetic disc apparatus. However, in the longitudinal recording method which is wide spread, a high-density recording brings about a problem of thermal fluctuation of recording magnetization due to a reduced recording bit size and a problem of a high coercive force which may exceed the recording head recording capability. Thus, a magnetic disc apparatus using a longitudinal recording medium has a limit as an apparatus for realizing a high-density recording. In order to solve these problems, a study has been conducted on a magnetic disc apparatus for mounting a vertical magnetic recording medium using the vertical magnetic recording method. As one of such magnetic disc apparatuses, there is provided a magnetic disc apparatus using a vertical two-layered medium consisting of a high-permeability soft film and a vertical magnetic film of a high vertical anisotropy.
FIG. 38 shows a conventional example of a magnetic disc apparatus having such a vertical magnetic recording medium. Moreover, FIG. 39 is a cross sectional view showing a conventional example of a vertical magnetic recording medium to be mounted on such a magnetic disc apparatus.
This conventional magnetic disc apparatus comprises: a conventional vertical magnetic recording medium 50 supported by a rotary spindle 33; and a slider 32 including a mono-pole/MR composite head 31 or an inductive/MR composite head 31 positioned on a recording track 35 and supported by an actuator 34. The vertical magnetic recording medium 50 includes a soft magnetic backing layer 52 and a vertical magnetization film 54 successively formed in this order on a substrate 56. For example, the soft magnetic film is a NiFe film, and the vertical magnetization film is a CoCr alloy film (see Japan Applied Magnetics Association Journal, Vol. 8, No. 1, 1984, p17).
It should be noted that as a related conventional technique, Japanese Patent Publication (unexamined) A-03-224122 entitled "Vertical Magnetic Recording Medium and Production Method of the Same" discloses a soft magnetic undercoat layer having means for suppressing magnetic domain wall shift.
Moreover, Japanese Patent Publication (unexamined) A-05-250651 entitled "Vertical Magnetic Recording Medium" discloses a soft magnetic layer constituted by an alphaFe16N2 film.
Furthermore, Japanese Patent Publication (unexamined) A-05-258274 entitled "Vertical Magnetic Recording Medium and Production Method of the Same" discloses a configuration providing a high-magnetic film having a residual magnetization between the substrate and the soft magnetic layer.
Moreover, Japanese Patent Publication (unexamined) A-05-266455 entitled "Vertical Magnetic Recording Medium" discloses a configuration using a three-layered soft magnetic backing layer consisting of a first soft magnetic layer film, a high magnetic film, and a second soft magnetic layer film.
However, in the magnetic disc apparatus of FIG. 38 having the vertical magnetic recording medium of FIG. 39, there is a problem that unstable recording magnetization with respect to an external magnetic field results in an unstable reproduction output.
The vertical magnetic recording medium of FIG. 39 includes an undercoat soft magnetic film 52 having a magnetic domain wall configuration. Accordingly, if a magnetic field is applied by some reason to the disc, even if a very weak magnetic field, the magnetic domain wall of the soft magnetic layer is easily shifted. If the wall shift occurs in a region corresponding to the main magnetic pole of the vertical magnetic head, the magnetization recorded in the vertical recording layer is reduced or demagnetized. Such a wall shift causing demagnetization is easily caused in a magnetic field in the parallel direction of the disc surface. Even for a magnetic field other than in a horizontal direction with respect to the disc surface, the magnetic field component of the horizontal direction is considered to function to cause demagnetization. This results in a reduction or disappearance of the reproduction output.
Such an external magnetic field is generated by a motor that controls the spindle 33 for rotating a disc positioned in the proximity of the magnetic disc and by a motor used for controlling an actuator 34 for positioning the head. Although these magnetic fields are very weak, if they are concentrated at the vertical magnetic head main magnetic pole tip, this will induce the domain wall shift of the undercoat soft magnetic film, which in turn causes demagnetization of the recording magnetization and the output reduction or disappearance. That is, a fatal defect is caused for the information recording apparatus.